A musculoskeletal model of a subject specific knee joint with menisci, during the stance phase of a walk cycle

Abstract

Movement simulation and musculoskeletal modeling can predict muscle forces, but current methods are hindered by simplified representations of joint structures. Simulations that incorporate muscle forces, an anatomical representation of the natural knee, and contact mechanics would be a powerful tool in orthopedics. This study developed a subject specific computational model of the knee with menisci within the multibody framework. The model was validated with experimental measurements from a mechanical knee simulator and then it was incorporated into a neuromusculoskeletal model of a lower limb. The detailed model of a subject specific knee was developed in MD.ADAMS (MSC Software Corporation, Santa Ana, CA). This model includes femur, tibia, patella as well as lateral and medial meniscus geometries and knee ligaments of a subject specific cadaver knee (female: 78 years old, 59 kg right knee). A deformable contact with constant coefficients was applied to define the contact force between patella, femur, and tibia articular cartilages. Meniscus geometries were divided into 61 discrete elements (29 medial and 32 lateral) that were connected through 6×6 stiffness matrices. An optimization and design of experiments approach was used to determine parameters for the 6×6 stiffness matrices such that the force-displacement relationship of the meniscus matched that of a linearly elastic transversely isotropic finite element model for the same cadaver meniscus. Similarly, parameters for compliant contact models of tibio-menisco-femoral articulations were derived from finite element solutions. As a validation step, the multibody knee model was placed within a dynamic knee simulator model and the tibio-femoral and patello-femoral kinematics were compared to an identically loaded cadaver knee. Consequently, the validated knee model was incorporated into a scaled lower right limb musculoskeletal model in LifeMODTM (Lifemodeler, Inc.). A forward-dynamics muscle driven simulation of the stance phase of a gait cycle was simulated to estimate muscles and ground reaction forces. The predicted forces were evaluated using test data provided by Vaughan CL. et al. (1999).